The Louche Effect is the name given when water is added to Ouzo and Abisnthe that turns the liquid into white. The science behind it is actually quite normal and tends to happen when adding essential oils to water. Effectively, what happens is that the water is reacting with a “hydrophobic” chemical in the reaction. Thujone, for example, the main flavoring in Absinthe is oil based and hydrophobic. Ouzo, as well, is made from Anise and fennel oil.

This effect was first described by Wilhelm Ostwald in 1896 and is known as the Ostwald Ripening effect. In simple terms,

The Ostwald Ripening effect occurs when an added ingredient creates a reaction that no longer puts the initial compound in equilibrium either due to the PH level changing, temperature changing and the number of common ions changing (the ability for the alcohol to bond with the oil). As alcohol and water share relatively the same PH level, the biggest changes in the Louche effect occur from temperature colder absinthe will cloud up faster than warm absent. Next, as more water is added, the Louche effect will become increasingly clear.